diff --git a/sys/malloc_thread_safe/malloc_wrappers.c b/sys/malloc_thread_safe/malloc_wrappers.c
index 138dae65a2..2fc390e1dc 100644
--- a/sys/malloc_thread_safe/malloc_wrappers.c
+++ b/sys/malloc_thread_safe/malloc_wrappers.c
@@ -14,13 +14,14 @@
  * @author  Gunar Schorcht <gunar@schorcht.net>
  */
 
+#include <string.h>
+
 #include "assert.h"
 #include "irq.h"
 #include "mutex.h"
 
 extern void *__real_malloc(size_t size);
 extern void __real_free(void *ptr);
-extern void *__real_calloc(size_t nmemb, size_t size);
 extern void *__real_realloc(void *ptr, size_t size);
 
 static mutex_t _lock;
@@ -44,11 +45,20 @@ void __wrap_free(void *ptr)
 
 void *__wrap_calloc(size_t nmemb, size_t size)
 {
-    assert(!irq_is_in());
-    mutex_lock(&_lock);
-    void *ptr = __real_calloc(nmemb, size);
-    mutex_unlock(&_lock);
-    return ptr;
+    /* some c libs don't perform proper overflow check (e.g. newlib < 4.0.0). Hence, we
+     * just implement calloc on top of malloc ourselves. In addition to ensuring proper
+     * overflow checks, this likely saves a bit of ROM */
+    size_t total_size;
+    if (__builtin_mul_overflow(nmemb, size, &total_size)) {
+        return NULL;
+    }
+
+    void *res = __wrap_malloc(total_size);
+    if (res) {
+        memset(res, 0, total_size);
+    }
+
+    return res;
 }
 
 void *__wrap_realloc(void *ptr, size_t size)